Use merge and merge_n from arrow-rs instead of custom implementations #19423
Description
Is your feature request related to a problem or challenge?
The implementations of merge and merge_n in case.rs have been moved to arrow-rs and a release of that crate with the implementations is now available. We should replace the versions in case.rs with calls to the implementation in arrow-rs now that it is possible.
Describe the solution you'd like
Replace the versions in case.rs with calls to the implementation in arrow-rs now that it is possible.
Describe alternatives you've considered
None
Additional context
No response